The present invention relates to a control system for preventing a vehicle, such as a skid steer loader, that has hydrostatic drive motors for the wheels, from rolling or creeping on an incline when the operator controls are in neutral and the vehicle should remain stationary. No independent brake needs to be applied. The vehicle has hydrostatic motors for the wheels. The motors are driven by pumps which are responsive to electrical signals controlled by an operator input, which can be changed to vary the ground speed. When the input control signal is zero, which indicates the vehicle should be stationary, any movement of the vehicle will result in a signal being generated that will be utilized to counterbalance the pressure created in the drive motors to cause the vehicle to remain stationary.
It is well known to use hydrostatic motors for driving industrial vehicles, such as self-propelled loaders. Hydrostatic drive systems utilize controls for variable volume flow of fluid between an inlet port of the motors, and an outlet port. The use of joysticks for controlling such vehicles also is well known, and the joysticks can be used for steering, speed control, and forward and reverse drive as well as loader lift arm and back tilt functions.
Controller systems with software implementation utilizing a plurality of inputs and providing signals to drive pumps are known as well.
An automotive type drive that utilizes a microprocessor for controlling hydrostatic transmissions is shown in U.S. Pat. No. 5,390,759, and a transmissions is shown in U.S. Pat. No. 5,390,759, and a control circuit for an all wheel drive vehicle is illustrated in U.S. Pat. No. 5,199,525.
A hydrostatic transmission that has a retarder valve that provides a braking effect if the motors are driven mechanically and begin to function as pumps, is shown in U.S. Pat. No. 3,913,453. The system shown in U.S. Pat. No. 3,913,453 does not provide for an actual stopping of the movement of the vehicle, but rather retards its movement.
The present invention relates to a control system for a vehicle driven by hydrostatic motors that will stop movement of the vehicle when the drive controls are in neutral. The drive circuit is a hydrostatic drive circuit which controls the flow of hydraulic fluid under pressure to the motors. The vehicle is a drive-by-wire vehicle where an operator control generates electrical signals provided to a digital controller that provides the signals for varying the drive pump speed and controlling the direction of movement.
In the self-propelled vehicle shown, two hydrostatic motors are used, one for the wheels on each side of the vehicle. The hydrostatic motors are preferably fixed displacement piston motors but can be variable displacement motors, and when the vehicle tends to roll, the motors will act as pumps and will create a back pressure in the system. Vehicle motion is sensed, with sensors called wheel sensors, preferably by sensing output axle or final drive rotation. The wheel sensor signals are used in the controller as a feedback for controlling the vehicle drive. The slightest motion can be detected, so motion of the wheels is resisted and the vehicle is held stationary.
When the operator control is at a zero velocity or stopped position, and the wheels roll to cause the drive motors to act as pumps, the wheel speed sensors signals are utilized in the controller to create a counter balance pressure at the input to the hydrostatic motors to counterbalance the higher pressure at one motor port that is created by a tendency to roll on an incline. The force or pressure balance is maintained to prevent unwanted motion.
The wheel sensors will provide signals to the controller not only indicating that the wheels are rolling, but also indicating the direction that they are rolling. The signal is used as an input to the controller, which will provide a signal to electrical displacement control pumps used to drive one or both motors provided on the skid steer loader illustrated, to balance the pressure being generated by the motor movement and stop the motor or motors from rotating.
The control system is based on electronic output from a joystick, or other operator controls that are used for operating the drive system. Wheel rotation direction and speed is sensed, and that signal is used to generate a control signal to the pump until roll is stopped.